In general in three-phase systems, any change in the voltage source during the phase causes the motors to reverse. Therefore, it is often necessary to know the phase sequence. Devices that control and determine the phase sequence are called phase sequence controllers. These devices are of two types: rotary type and static type.

In three-phase systems, the phases are generally indicated by the letters R, S and T. When a three-phase electric motor is connected to the grid in sequence R, S and T, the motor rotates clockwise. When the connections are reversed, this direction of rotation of the motor is also reversed.

The main operating principle of the rotary type phase sequence controller is like the operation of asynchronous motors. The windings and their connections are marked R, S, T. When three phase energy sources are connected to these connections, a rotary magnetic field is formed in the windings and this rotary magnetic field generates an electric motor force. With this force, the aluminum disc inside starts to rotate. If the disc rotates clockwise, the sequence of the phases is R, S and T. The static type phase sequence controller has no moving parts. It is understood that the phase sequence is in the form of R, S and T with the help of indicator lamps.

In order to control the sequence of the three phases feeding the motors, a device called phase sequencing relay has been developed. If the R, S and T phases are in the correct order, the light on the front panel of the device is lit. This light goes off when there is a change in phase sequence. The phase sequence relay is used to protect elevators, air compressors and three-phase motors in similar systems.

Our company, within the framework of electrical safety examinationsconducts its phase sequence measurements in accordance with the relevant legal regulations, standards and test methods published by domestic and foreign organizations. The standard considered in these studies is:

• TS EN 61557-7 Electrical safety in low voltage distribution systems - Up to 1 kv AA and 1.5 kv DA - Equipment for testing, measuring or monitoring protective devices - Part 7: Phase sequence